The basics: a good answer:
actually answers the question
shows the work, so that people don't just have to take your word for it. This can be sources, a logical explanation, or any other path from the text to the answer. This is not a rigorous requirement, but "random user on the internet says so without explanation" isn't helpful. Unsupported (in any way) = bad.
is thorough (not a one-liner or a link-only answer)
is comprehensible: coherent English, reasonable formatting, etc
includes relevant quotes from the text instead of just citing (not required, but it sure is helpful!)
That's all in Jack's answer too, and is pretty common Stack Exchange guidance. I hope none of that is controversial.
In order to distinguish itself from specific-religion-flavored bible sites, Yahoo Answers, and churches, this site should be about the text, like it says in the FAQ.1 If the chain of logic in your answer isn't driven by the text, it's not a good answer for a text question. What you believe, what you want it to say, what your pastor says it means -- these are not relevant (though your pastor is a weak source if you cite). A good answer could even offer an interpretation that is contrary to the beliefs of the answerer.
This isn't to say that we all need to check our beliefs at the door. Most people wouldn't be here if we didn't strongly hold some deep religious beliefs. But an answer that depends on a particular religious perspective is not useful to the community, only to believers of that perspective, and there are better places to get belief-centric answers. Further, it'll lead to, as Jon put it, "knife fights in the comments". We are better than that.
I think the only way for our site to be viable -- to be open to a broad range of users like we say we want, to be civil and harmonious, and to build a body of useful content -- is to adopt a variant of Neutral Point Of View (NPOV). Specifically, good answers:
- Avoid stating opinions as facts.
- Avoid stating seriously contested assertions as facts.
- Avoid presenting uncontested factual assertions as mere opinion.
- Prefer nonjudgmental language.
Bad answers do the reverse of those.
These are not hard requirements. They are elements of polite society. Nobody should be leaving the site over this.
The NPOV writing style does come with a learning curve, but so does using Stack Exchange at all. We're all here to help each other. The difference between "that's a clear reference to Satan" or, more subtly, "because of the satanic influence, this means..." and "according to Luther, this means Satan because..." is not a large one. (If it's too large for some, leave off the "because..." -- at least you grounded it.) As a cost of doing business, we have to recognize that our users subscribe to multiple Truths, with conflicts deep enough that people have led holy wars and pogroms over them, and we should want no part of that, not even to sow the seeds of the seeds of disrespect.
(The Wikipedia article describes one other requirement that it is not reasonable to impose on individual answers: Indicate the relative prominence of opposing views. That's a fine goal for a community of editors working on a single Wikipedia page, but it's too much to ask of contributors here. If an answer supports its view well, and other answers support theirs, that is enough.)
One important difference between my proposal and Wikipedia is this:
This doesn't mean that you can't express an opinion along with your answer. It just means you have to label it as your opinion. We have plenty of answers that lay out some evidence and then say "I understand this to mean X" or "according to (my religion) this means Y" or even "I think that's clearly Z". I don't want to lose those answers, so long as they're not just that. Stack Exchange wisdom calls on us to be scrupulous about what we know and don't know; here, we need to be just as scrupulous with our opinions (what we "know", if you will).
A Case Study
At the risk of appearing arrogant (not my intent!) or calling down the wrath of contrarians (I do hope you'll show restraint), I'd like to look at some data to back up what I'm saying.
I'm a high-rep user. Based on visual scan, I have more than 5K of reputation from answers, which might even be more than Jon. At this writing, every single one of my 97 answers is up-voted, and I have more Nice Answer badges than anybody else (by half-again). It appears that the community thinks pretty well of my answers.
And this is the style I strive for. Do I always succeed? Probably not, and please do comment on answers that could be better in this regard so I can fix them, but I seem to have a decent track record. So maybe this is weak evidence, but I think it's proof by example that neutrally-written answers (1) are possible and (2) are well-received by the community.
The guideline I'm proposing is not too hard; it is not in heaven or across the sea; it is very close, within reach, for all who care to engage with us.
1: This site is also about hermeneutical methods. Those questions won't start from the text, though they may use textual examples. I've been talking here about the text; it is possible that "method" questions are, err, "squishier" than text questions, and I don't know enough to make that call. Since the vast majority of our questions are text, I don't think we need to tackle this now.